1. Field of the Invention
The present invention relates to image reading devices and method, and image forming apparatus and method.
2. Description of the Related Art
Prior image forming apparatus compatible with A0 size subject paper uses only one close image sensor (referred to as “CIS” hereinafter). That is, such a prior image forming apparatus uses a CIS having a length of A0 size paper width to read an original subject. However, such prior image forming apparatus is very large and takes high manufacturing cost, resulting in high price of the image forming apparatus.
Therefore, as shown in FIG. 1, an image forming apparatus having 5 CISs equivalent to A4 size paper arranged zigzag is already known.
In order to accurately read the original subject and obtain good results, it is necessary that the image forming apparatus should correctly recognize white color as reference. Accordingly it is required to adjust the image forming apparatus to make it properly recognize the white color that is called “white color reference adjustment”. The white color reference adjustment is a process wherein an output of the CIS reading light generated by a light source is adjusted (gain adjusted) to a predetermined output reference value by an amplifier (or a signal amplifier) before image forming.
Since a prior image forming apparatus compatible with A0 size paper has only one large CIS, even if a problem occurs in white reference adjusting, it is easy to re-adjust the white reference for the only one CIS during the following image processing step.
Patent Reference 1: Japanese Patent Laid-open Publication 2001-157006
However, a prior image forming apparatus compatible with A0 size paper having plural CISs arranged zigzag, has only one amplifier (or signal amplifier), and therefore can adjust one white reference for only one CIS (e.g. CISm shown in FIG. 2), and the other CISs cannot be adjusted, resulting in variations in CIS outputs.
As a result, each CIS has a different white color reference, and when the same white color is read by plural CISs, some CISs output grey color, providing bad image forming.